Method of the Particle-in-Cell Simulation for the Y-point in the Pulsar Magnetosphere

TL;DR

This paper introduces a new Particle-in-Cell simulation code tailored for the Y-point in pulsar magnetospheres, revealing dynamic structures and plasma behaviors that could explain observed high-energy emissions.

Contribution

The paper presents a novel 2D-3D Particle-in-Cell code for the Y-point in pulsar magnetospheres, incorporating relativistic particle motion and specialized boundary conditions.

Findings

Identification of a variable Y-shaped structure at the light cylinder

Evidence of magnetic reconnection and plasma heating near the Y-point

Breakdown of ideal-MHD conditions in the Y-region

Abstract

Recent observations in X-ray and Gamma-ray suggest that the emission region of the pulsar magnetosphere can be multifold. In particular, the open-close boundary of the magnetic field, so-called the Y-point, can be the new candidate place where magnetic field energy converts into the plasma heat and/or flow energy. Here, we present a new Particle-in-Cell code, which can be applied to the Y-point of the pulsar magnetosphere in axisymmetric geometry. The electromagnetic solver is used in the two-dimensional grid points with the cylindrical coordinate (R, z), while the particle solver operates in the three-dimensional Cartesian coordinate (x, y, z), where the Buneman-Boris method is used. The particle motion is treated in special relativity. The inner boundary conditions are set up to generate rotation of the magnetosphere by use of the force-free semi-analytic solution given by Uzdensky (2003, ApJ, 598, 446). The code has been verified by dispersion relations of all the wave modes in electron-positron plasmas. The initial test run is also presented to demonstrate the Y-shaped structure at the top of the dead zone on the light cylinder. We suggest that the structure is variable with quasi-periodicity associated with magnetic reconnection and that plasma will be accelerated and/or heated. In a time-averaged point of view, break up of the ideal-MHD condition takes place in the vicinity of the Y-point.